Externally pressurized fluid bearing



March 15, 1960 H. K. BAUMEISTER 2,928,709

EXTERNALLY PRESSURIZED FLUID BEARING 2 Sheets-Sheet 1 Filed Nov. 7. 1955FIG.2

INVENTOR. I HEARD K. BAUMEISTER god 11w FIG.3

AGENT March 15, 1960 H. K. BAUMEISTER 2,923,709

I EXTERNALLY PRESSURIZED FLUID BEARING Filed NOV. 7, 1955 2 Sheets-Sheet2 FIG.5

55 INVENT m 54 HEARD K. BAUM ER BY Z AGENT 2,928,709 1C6 Patented Mar.15, 1960 EXTERNALLY PRESSZED FLUID BEARING Heard K. Baurneister, NewYork, N.Y., assignor to Intel-national Business Machines Corporation,New York, N.Y., a corporation of New York Application November 7, 1955,Serial No. 545,266

2 Claims. (Cl. 346-74) This invention relates to slider bearings of theexternally pressurized type and more particularly to floating shoe typebearings adapted to support a magnetic recording head.

Heretofore, magnetic recording heads have been supported by air bearingsutilizing the familiar Bernoulli effect. This type of airbearing'comprises a shoe having a surface, referred to as the sillsurrounding a recess referred to as the pool, which is in juxtapositionwith a moving surface such as a rotating magnetic drum or disc. Air issupplied to the shoe by means of a hole bored therethrough and orientedorthogonally to the sill area surface. The air is supplied to thebearing surfaces at a constant pump pressure, the force provided by theair in the pool and from the high velocity escaping air over the sill,opposes the force of the atmosphere on the other side. The shoe existsat a predetermined distance from the drum when these forces aresubstantially equal. When the relative velocity of the surfaces is zero,for example, and the spacing therebetween is large, the wellknownBernoulli effect causes a reduction in pressure over the sill area so asto permit a decrease in the spacing. However, when the spacing is smallthere exists a more linear pressure gradient over the sill area whichforces the surfaces apart until the sill and pool pressures and theexternal atmospheric pressure are equalized, and the shoe reaches astable position.

Thus although the pressure of the air supplied to the shoe is constant,it tends to maintain a predetermined distance between the surface of theshoe and the surface of the magnetic drum.

The chief disadvantage of the Bernoulli type bearing referred to aboveis that the pump pressure and therefore the pool pressure issubstantially constant. Another disadvantage is that the spacing betweenthe shoe and the drum is rather large. A further disadvantage exists inthat the maximum force which can be utilized to maintain a constantspacing by such a shoe operating in atmospheric pressure is quite smalland could never be greater than 14.7 lbs. per square inch.

Accordingly, it is an object of the present invention to provide a novelbearing capable of utilizing a force in excess of that fraction of 14.7lbs. per square inch, which due to the inertia of the shoe andeccentricity of the drum, will thereby maintain a more constant spacingand also permit a smaller spacing.

Briefly, the present invention comprises a shoe having a bearing surfacewhich coacts in a very different manner than before with a movingsurface, as for example, a rotating magnetic drum, disc or tape, etc.The bearing surface of the shoe, referred to as the sill area,intersects a recessed chamber or pool encompassed by the shoe. Alubricant under pressure is supplied through a restrictor to the pool.With the drum at rest, for example, the shoe assumes a stable positionwhere the effective pressure P (gauge) in the fluid over the whole shoearea A.

is sufficient to sustain the externally applied loading force F. Theeffective pressure P is due to the pool pressure and the hole.

1" and the sill pressure P A change in the distance between the surfaceof the drum and the bearing surface of the shoe permits an alteration inthe effective pressure to occur whereby the force exerted against thedrum causes the shoe to move towards the stable position. For anyposition of the shoe other than the stable position, the pressure in thepool and over the sill changes in such a manner that the product of theeffective pressure times the shoe area is temporarily different from theexternally applied loading force F. This imbalance of the forces tendsto move the shoe towards the stable position.

Thus since the effective pressure in the pool as well as over the sillis capable of changing and does not need to be in any part constant, thebearing tends to maintain very closely a predetermined distance betweenthe shoe and the drum. The presence of the restrictor allows the poolpressure P to change without requiring that the pressure at the pump orsource of the lubricant be altered.

The load carrying capacity of the bearing can be increased by increasingthe pump pressure. In addition, since the novel bearing is capable ofsupporting greater loads than a similar Bernoulli type bearing, thespacing between the novel 'shoe .and the drum may be smaller than ispermissible with the Bernoulli type bearing.

'Since the sill area of the present invention may be smaller thanpresently known shoes the coefficient of friction between the bearing.surfaces. could be made smaller.

One embodiment of the invention includes a novel restrictor which may beincorporated within the structure of the shoe. The restrictor includes aremovable plug assembly which may be removed so that the restrictor canbe cleaned or easily'changed. The novel restrictor includes thedumbbell-shaped plug having a center rod and two larger ends which isinserted into a hole drilled into the shoe. The diameter of the rod isslightly smaller than the diameter of the hole so that the fluidlubricant may flow in the space between the peripheries of the rod Thelarger ends merely serve to center the rod in the hole. The amount ofrestriction to fluid flow provided by the restrictor is governed by theamount of space existing between the rod and the inside diameter of thehole.

Another object is to provide an improved externally pressurized shoetype hearing which maintains a predetermined distance between thebearing surface of the shoe and the bearing surface coacting therewith.V

A further object is to provide a novel multi-pad externally pressurizedbearing capable of operating with air or oil as the fluid lubricant.

It is also an object to provide a recording head which floats on andfollows a magnetic surface despite displacements due to the eccentricityand non-circular cross section of the drum, disc, tape drive capstans,etc.

Another object is to provide a highly stable air lubricated shoe forsupporting a recording element.

A still further object is to provide an externally pressurized sliderbearing having one or more pads, each pad having a restricter coastingtherewith whereby a change in the distance between the bearing surfacescauses a change in the pressure of the lubricant within each pad so asto restore the bearing to a stable parallel condition.

A further object is to provide a novel restrictor.

It is also an object to provide a novel restrictor which is considerablysmaller than a restrictor composed of coiled tubing.

Another object is to provide a novel restrictor which supplies two poolssimultaneously.

An additional object is to provide a restrictor contained within abearing block or shoe so that the restrictor is not susceptible tofracture as is the case with a copper tubing restrictor which isconstructed external The lubricant enters the shoe at the point 36 andexhausts through the spacing 37 between the surface of the Anotherobject is to provide a restrictor which acts as a filter to lodge dirtand dust particles and which is capableof being cleaned so as to removeany particles filtered outof the fluid lubricant.

Another object is to provide a novel restrictor which is incorporatedwithin a bearing plug or shoe wherein said shoe defines ahollowdiametercomprising a first member of-the restrictor and a secondmember which isdesigned to fill a substantial portion of the volume of said firstmember and said restrictor being provided with inlet and outlet meanswhereby a fluid lubricant is supplied to and removed from therestrictor.

Another objectis to provide a novel externally pressurized, fluidlubricatedbearing including a shoe having a bearing surface whichincludes a chamber, a restrictor and means for. supplying a pressurizedfluid lubricant through said restrictor to said chamber and thus to'thebearing surfaces.

shoe '27 and the surface of the drum 21. As will be explained presently,the exhausting lubricant causes a predetermined spacing to be maintainedbetween the bearing surfaces of the shoe and the surface of the drum.The distance between the bearing surface of the shoe and the surface ofthe drum is dependent upon the external loading force applied to theshoe 27 by means of the leaf spring .24 and the pressure of the. fluidsupplied to the sho It is not necessary to provide a retractingmechanism for lifting the shoe off of the drum when the drum is Otherobjects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of example, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.In the drawings: V Fig. 1 illustrates the novel hearing whichincorporates a single pad and utilizes an external restrictor;

Fig. 2 is a cross section of Fig. l and thus illustrates the internalconstruction of the bearing; I Fig. 3 illustrates the equivalentelectrical circuit of the mechanical system of Fig. 2;

Fig. 4 illustrates a novel bearing which incorporates a plurality ofpadsand an internal restrictor;

Fig. 5 is 'a cross section of Fig. 4 and illustrates the" which is notillustrated. A mounting bar 22 is provided which is rigidly attached toany suitable external-framework. A leaf spring 24 is fastened to theunderside of the mounting bar 22 and extends towards the surface, of thedrum in a substantially tangential direction. Leaf spring 24 ispro-stressed or pre-bent. The other extremity of the leaf spring 24 isbifurcated and the separate extensions 25 and 26 span the shoe 27 andencircle a pair of trunnions 28 which extend from the shoe 27. Themounting bar 22 is secured to the external mechanism not shown ordescribed herein so that the leaf spring 24, which may be pre-bent,applies a loading force to the shoe 27 which tends to force the shoetoward the surface 21 of the drum. e

A magnetic recording element or transducer 30 is mounted on the shoe 27so that the gap of the yoke 31 is adjacent to the recording surface 21.The head structure is fastened to the shoe by means of set screws whichclamp the laminated yoke 31 against one side of the shoe. The yoke mayalso be mounted on the shoe in any other conventional manner.

A fluid lubricant at a constant pressure is supplied to the pipe 34 andthrough the'restrictor ,35 to the shoe.

stopped, providing that the fluid lubricant is continuously supplied tothe head. The presence of the flowing lubricant maintains apredetermined spacing between the head and the recording surface evenwhen said surface isstationary. Thus when the drum is stopped the shoecannot mar or score the drum surface.

The escaping air aids in preventingthe' accumulation of dirt in thespacing between the head andthe drum.

Due to possible eccentricities of the drum 20, the shoe 27 may besubject to rocking motions about the trunnions 28 and also tomotionabout the axis 23. This flexibility permits the shoe 27 to maintain aconstant space relationship between the surface of the shoe and the drum21 despite irregularities which may appear along the drum surface.Furthermore, the shoe 27 is capable of a tipping motion due to theindividual extensions 25 and 26 of the leaf spring 24. It should beappreciated that mechanisms other than the leaf spring 24 and themounting bar 22 may be. used to suspend the shoe 27 over the drumsurface. Fig. 1 may be supported by the type of mounting illustrated inFig. 3 of application Serial No. 406,448, filed January 27, 1954 by H.K. Baumeister.

Referring more particularly to Fig. 2, a cross section of rearwardportion of the shoe 27 is illustrated. The extremity ofthe restrictor 35of Fig. 1 is connected to the shoe27 at the point 36 as indicated inFig. 2. The fluid lubricant flows downward through a channel 01' hole40*extending through the shoe to a pool or chamber 41. f

The poolis also referred to as a lubricating pad. After filling the pool41, the lubricant exhausts at the points 37 between the'bottom surfaceof the shoe and thesurface 21 of the'drum. The pool 41, which isrecessed in the bottom surface of the shoe 27, may comprise a volume ofany suitable configuration. The bottom surfaces 42 of the shoe 27 whichare not recessed are referred to as sill areas.

In order for a predetermined space relationship to be maintained betweenthe surface 42 of the shoe and the drum surface 21, the externallyapplied force F must be equal to the effective pressure P times the areaA of the shoe which is juxtapositioned with the drum surface. When thisrelationship is disturbed, the space relationship betweenthe shoe andthe drum recording surface will be increased or decreased. In order forthe shoe to be returned to the stable position wherein F is equal toPA,.the effective pressure must be altered so that it is properlyincreased or decreased as required. The area of the bottom surface ofthe shoe comprises the 'sill area A and'the pool area A,,. The efiectivepressure P of the lubricant which is exerted against'the surface of thedrum is due to the pressure beneath the sill areas P and the pressure Pwhich exists within the For'example, the shoe 27 of If, for example, thespacing between the surface of the shoe and the drum surface isdecreased temporarily, the effective pressure P must be increased so asto provide a greater force which will tend to restore the shoe to itsnormal stable position. Also, when the distance between the shoe anddrum surfaces is increased temporarily, the effective pressure must bedecreased so that the shoe will tend to return to its normal stableposition, thereby decreasing the spaced relationship of the shoe and thedrum to the normal distance. A change in the distance between the drumand shoe bearing surfaces causes the sill pressure P and the poolpressure P to be adjusted so that the shoe is restored to its normalstable position. The presence of the restrictor 35 of Fig. 1 permits thepool and sill pressures to be adjusted even though the pressure at thesource of the lubricant remains constant. The removal of the restrictorprohibits the shoe from functioning in the manner described above.

Referring more particularly to Fig. 3, the electrical analogy of thesingle pad shoe of Figs. 1 and 2 is illustrated. The resistance B is afunction of the restriction or resistance to fluid flow provided by therestrictor 35 of Fig. l and the resistance R is a function of theseparation 37 (Fig. 2) between the shoe and drum surfaces.

The voltage V of Fig. 3 is related to the pressure at the pump or sourceof lubricant and is considered to be a constant. The voltage V is afunction of the pool pressure P The current flowing through theresistors B and R is a function of the quantity of fluid lubricantsupplied to the shoe of Figs. 1 and 2. It is apparent from theelectrical analogy that the maximum change in P with respect to thefactor R occurs when the mechanical design of the shoe is such that thefactors R and B are equal. It is desirable to obtain the maximum changein the pool pressure 1? with respect to the separation of the drum andshoe surfaces in order to obtain a highly sensitive bearing. It isdesirable that the bearing of Figs. 1 and 2 be highly sensitive so thata change in the distance between the shoe and drum surfaces is correctedand the shoe returned to its stable position as rapidly as possible.

The electrical analogy also points out that the purpose of therestrictor is to permit a pressure drop to occur between the source ofthe lubricant and the pool or pad of the shoe. The pressure within thepad must be capable of increasing or decreasing as the spacing betweenthe bearing surfaces changes. That is, when the spaced relationship ofthe surfaces is increased due to an irregularity in the surface of thedrum, the pool pressure must decrease and similarly, when the spacing isdecreased, the pool pressure must increase so as to reestablish thestable position of the shoe. The restrictor could be removed from thesystem only if the constant pressure source of lubricant is replaced bya device which provides a constant quantity of lubricant flowing in thesystem. Since it is diflicult to provide a constant quantity lubricantsource, the use of the restrictor considerably simplifies the system andthe external pumping apparatus which must be used to supply the fluidlubricant.

Since the externally applied force F is equal to the product of theeffective pressure and the area of the shoe, it is apparent that byincreasing the load applied to the shoe, the spacing between the bearingsurfaces of the shoe and the drum can be decreased.

The externally pressurized bearing described herein operatessatisfactorily where the lubricant is air, oil or another suitablefluid. The description hereinabove of the operation of the bearing ofFigs. 1 and 2 applies asserts 6 lubricant is air but will not operate insuitable manner when the lubricant is changed to oil.

It has been determined experimentally that when the shoe of Figs. 1 and2 is provided with a relatively wide sill area in the direction that therecording surface is moving, a cubic relationship exists between theresistance to flow of the lubricant between the bearing surfaces and thespacing between said surfaces. As the sill area is made'smaller andapproaches a knife edge, the relationship between the resistance to flowand the spacing of the bearing surfaces is a square or even a directrelationship depending on the fluid properties. son, the resistance toflow in a shoe having a wide sill area is C /h whereas the relationshipis Cg/h when the sill area is very narrow, where C and C are arbitraryconstants and h is the distance between the bearing surfaces of the shoeand the rotating drum. Accordingly, it is apparent that where theresistance to flow is inversely proportional to the cube of the spacingbetween the bearing surfaces, a given change in spacing h, produces agreater change in the pool pressure P than would occur where therelationship Cg/h obtains. This aids in making the head more sensitiveto changes in spacing and thus is another factor which increases thesensitivity of the shoe.

' Referring to Fig. 4, a second embodiment of the invention isillustrated which incorporates within the head a novel restrictor. It isapparent that when the restrictor comprises a long section of coiledtubing as shown in Fig. 1, difliculties are encountered in mounting theassembly on the head since the tubing is subject to fracture.Furthermore, the restrictor 35 of Fig. 1 occupies a space which is oftenquite large compared to the space required by the shoe and headassembly.

These difliculties are overcome by constructing the restrictor withinthe shoe as indicated in Figs. 4 and 5 :hich illustrate a restrictorsupplying two pools with no greater difficulty than would be required tosupply a single pool. In Fig. 4 the lubricant under constant pressure issupplied to the tube 46 which is connected directly to the shoe at thepoint 48.

Fig. 5 is a cross section of the shoe 47 of Fig. 4 taken at the pointindicated. In Fig. 5 the tubing 46 which carries the fluid lubricant issuitably connected to the 7 shoe 47 at the point 48 by means of athreadable connection or other well-known methods. The fluid containedwithin tube 46 flows downward through the channel or hole 49 to therestrictor.

The restrictor comprises a hole 52 extending into or through the shoe47. The hole is threaded at the points 53 so as to accept the threadedcaps 55, which, in this design, are used to seal the ends of the hole. Adumbbell assembly 54 is inserted into the hole and retained therein bythe caps 55. The dumbbell assembly 54 is illustrated in Fig. 6. The rod56 is connected to the collars 57 and 58 which serve to center the rodin the hole 52. The diameter of the rod 56 must be slightly smaller thanthe inside diameter of the hole 52 so as to provide a predeterminedclearance therebetween. The diameter of the collars 57 and 58 issufiiciently smaller than the diameter of the'hole 52 to allow the plug56 to be inserted therein. The difference between the diameter of therod 56 and the hole 52 determines the resistance to flow of thelubricant flowing through the restrictor. As the diameter of the rod 56is decreased, the resistance to flow offered by the restrictor to fluidflow is decreased.

The fluid lubricant applied to the restrictor through inlet hole 49 ofFig. 5 flows through the space 52 existing between the periphery of therod 56 and the hole 52 and exits through the outlet holes 60 and 61.These outlet holes connect the restrictor with the pools or pads 62 and63. A pressure drop may occur across each half of the restrictor so thatthe pressure in pools 62 and 63 is lower than the pressure existing inthe supply tube 46 and the inlet hole 49. The fluid then escapes fromthe By way of comparispasm-a P9 15 and 6 t o h the s ce- 37 xi n e eenthe bearing surfaces of the shoe and the magnetic drum.

it is to be noted that the restrictor illustrated in Fig. 5 serves bothof the pools 62 and 63. It is apparent that if a shoe contains a singlepool, the restrictor of Fig. 5 could be used by merely placing the inlethole 49 at the opposite extremity of the restrictor from the location ofan'outlet hole such as outlet hole 60. Other variations of therestrictor arealso possible depending upon the construction of the shoe.For example, the restrictor might also be constructed in'a verticalposition so that the cap 55 of Fig. 5 appears in the topsurface of theshoe assembly. i

Afirst advantage of'therestrictorof Figs. 5 and 6 is that it isconsiderably smaller than restrictors now known in the. art oflubrication engineering." For example, a

magnetic transducer in spae'ed relationship with a recording surface"including the'combination er, aia pidly,

moving bearing surface, a bearing shoefh'aving a recess, a magnetictransducer supported'by said shoe and ar; ranged in spaced relationshipwith respect to said moving bearing surface, means urging said shoeagainst said bearing surface, a second bearing surface surrounding saidrecess and existing in juxtaposition with said first surface to floatthereon, an external source of pressurized lubricant, and meansfor'supplying said lubricant to said recess of said'shoe therebycreating a force in opposition to the urging means .so that said shoefloats on said' bearingjsurface including means for effecting anadjustment of the pressure of the lubricant within said recess inresponse to a change in separation between'said second bearing surfaceand said first bearing surface to restrictor. of the type illustrated inFig. 5 having a total 7 length of one inch and a radial clearance of0.001inch will provide a resistance tofluid flow substantially equal tothat provided by a coiled copper tubing restrictor of the typeillustrated in Fig. 1. which comprises approximately 477 feet of tubing,having an inside diameter of 0.1 inch. The restrictor of Fig. 5 is alsoequivalent to a restrictor comprisingta hole having a diameter of 0.0135inch and approximately 12.4 inches long. The latter type restrictor isimpractical and difficult to construct.

A further advantage of the restrictor of Fig. 5 lies in the factthat itcan be constructed within the shoe 47 and thus is not subject to damageor fracture as is the case with an exposed coiled tubing restrictor ofthe type illustrated in Fig. 1. Where the hole 52 of Fig. 5 has adiameter of approximately 0.25 inch item be drilled and reamed in theshoe'within very small tolerances. Likewise, the plug 54 can be machinedto small tolerances so that the difference between the diameters of therod 54 and the hole 52 is of the order of 0.001 inch.

Another advantage of the novel restrictor of Fig. 5

is that the plug assembly of Fig. 6 can be removed for cleaningpurposes. It is frequently impossible to clean a restrictor of the typeillustrated in Fig. 1 which has become clogged by large dirt particles.

An additional advantage of the restrictor described 1 vention as appliedto a preferred embodiment, it will be understood that'various, omissionsand substitutions and changes in the form and details of thedeviceiillustrated and in its operation may be made by those skilled inthe art without departing from the spirit of the invention. It is theintention, therefore, to be limited only as indicated by the scope ofthe following claims.

What is claimed is: r

1. In a magnetic recording system for supporting a counteract saidchange, the said adjustment effecting means being contained within saidbearingshoe, the said shoe defining a substantially cylindrical chamberof pre: determined length having fluid entry and exit pcrts, alongitudinal member having a s'rnaller' diameter 'than said chamber andinserted therein to provide a spacing between the outer surface of saidlongitudinal member and the inner surface of said chamber in the rangeof one to five thousandths of an inch, and means for main taining apredetermined distance between the periphery of said longitudinal memberand the inside surface of said chamberto provide a pressure differentialbetween said entry and exit ports, whereby the spacing between said shoeand said recording surface is maintained submember contained within saidchamber and occupying a smaller volume for producing a pressuredifferential between said pad and said source whereby a change inspacing between said, recording surface and the surface of said firstmember is counteracted by'a change in said pressure differential toadjust the pressure in said pad thereby re-establishing the originalspacing between said transducer and said recording surface.

References Cited in the file of this patent UNITED STATES PATENTS1,619,444 Taylor Mar. 1, 1927, 2,038,216 Harrison et al. Apr. 21 19362,415,992 Clair Feb. 18, 1947 2,612,566 Anderson Sept. 30, 19522,695,199

Blizard Nov. 23, 1954-

